A primary objective of lubrication systems is to supply a constant rate of lubricant, such as oil, to a mechanical system. Among lubrication systems currently in use are `active` and `passive` systems. Active systems typically employ pumping devices that control the volume of oil being pumped, such as volumetric and peristaltic pumps. These systems are expensive and unwieldy. Passive systems are based on gravitational drip of the oil and typically consist of a container for the oil, a needle valve to control the flow thereof, and a nozzle and conduits for administration thereof. These systems are much simpler and less expensive than the active systems, but have the disadvantage in that they have no way to maintain a constant oil drip rate. The oil drip rate in such systems varies significantly with variations in the viscosity of the oil, which may result from changes in temperature such as occur between day and night, and with variation in the height of the oil in a container or its static pressure head, as the supply is depleted. The nozzle and conduits are also subject to blockages, partial and full, caused by particulate impurities in the lubricant.
U.S. Pat. No. 4,428,442 discloses a lubricating system for normally air-lubricated mining bits in which oil is forced under pressure into the relevant passages. This system is not concerned with gravitational flow of lubricant or with the solving the problem of maintaining a constant rate of lubrication.
U.S. Pat. No. 5,598,973 discloses a flow control mechanism in liquid dispensing guns in which a threaded shaft may be rotated in opposing rotational directions by electrically powered drive means in order to operate a valve between a full flow position and a number of reduced flow positions. Although the system may be operated to counter viscosity changes and blockages, there is no suggestion to adapt the system to controlling the drip rate of a gravitational flow lubrication system.
There are a number of patents dealing with the control of the rate of administration of a liquid medicament to a patient via gravitational drip systems, such as in intravenous infusion systems. U.S. Pat. Nos. 3,790,042 and 4,038,982 disclose systems in which the drip rate in a fluid drip chamber is measured and a valve or clamp controlling the rate of fluid administered is automatically opened or closed to maintain a desired drip rate. In their details, these systems are specific to medical applications and do not deal with problems inherent in lubrication of mechanical systems.